1. Field of the Invention
The present invention relates to an improved getter pump of the modular type employing non-evaporable getter materials embedded in a substrate. A modular getter pump according to this invention is particularly suitable for use either alone or as a multiple array in order to sorb gases in closed containers in which it is desirable to produce and maintain a high vacuum.
2. Description of the Prior Art
Getter pumps employing non-evaporable getter materials embedded in a substrate are known and have found wide acceptance for producing and maintaining vacuums in closed vessels. See for example U.S. Pat. Nos. 3,609,062; 3,662,522; and 3,780,501. In particular, getter pumps employing a substrate of high ohmic resistance and a non-evaporable getter material embedded in the substrate have been described in U.S. Pat. No. 3,609,064. Such getter pumps usually employ a substrate in the form of a long ribbon, previously coated with non-evaporable getter metal particles as described in U.S. Pat. No. 3,652,317. The long ribbon is then folded repeatedly backwards and forwards to form a pleated substrate which is then disposed radially about a central axis. A resistance heater is frequently provided in coincidence with said central axis.
Even when a separate heater is not provided, as in the case of a getter pump comprising a substrate of high ohmic resistance, the preferred form of a substrate is a pleated strip. See for example Column 1, Line 60, and FIGS. 1 and 2 of U.S. Pat. No. 3,609,064. Unfortunately, such devices suffer from a number of disadvantages. The presence of the necessary separate resistance heater increases production costs. Uniform heating of the getter metal is difficult if not impossible to obtain since various portions of the coated substrate are at varying distances from the separate resistance heater. Furthermore, a separate heater is inefficient due to excessive heat loss to parts which are not intended to be heated thus wastefully increasing the power requirements of the getter pump.
Furthermore, if a large surface area has to be rendered capable of sorbing gases, then it becomes cumbersome to cover this entire surface area with prior art non-evaporable getter pumps.
Another method of pumping unwanted gases is by causing them to condense on panels cooled to cryogenic temperatures. However, this involves the use and handling of expensive cryogeni liquids. Very often, the cooled surfaces have to be shielded by chevron baffles or the like, to prevent re-evaporation of condensed gases, and screened against evergetic particle bombardment. Such baffles can undesirably limit the pumping speed of the panel. Moreover, cryogenic pumps, if exposed to a pressure increase caused by system leaks or failure, can abruptly desorb previously sorbed gases, thus leading to production of an explosive air-hydrogen mixture. Constraints are placed on the spacial orientation of the condensation panels imposed by the fact that the cryogenic coolant is a liquid.
Accordingly, it is an object of the present invention to provide a getter pump which required no separate heater, thus reducing the power requirements and cost of the pump. Still another object is to provide a getter pump which can be assembled to cover large surface areas and be capable of replacing cryogenic pumping units. A further object is to provide modular getter pumps which can be placed together to conform to the interior surface of a vacuum vessel in any desired spacial orientation.